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Effects of strand and directional asymmetry on base-base coupling and charge transfer in double-helical DNA

机译：链和方向不对称对双螺旋DNA中碱基-碱基偶联和电荷转移的影响

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Mechanistic models of charge transfer (CT) in macromolecules often focus on CT energetics and distance as the chief parameters governing CT rates and efficiencies. However, in DNA, features unique to the DNA molecule, in particular, the structure and dynamics of the DNA base stack, also have a dramatic impact on CT. Here we probe the influence of subtle structural variations on base-base CT within a DNA duplex by examining photoinduced quenching of 2-aminopurine (Ap) as a result of hole transfer (HT) to guanine (G). Photoexcited Ap is used as a dual reporter of variations in base stacking and CT efficiency. Significantly, the unique features of DNA, including the strandedness and directional asymmetry of the double helix, play a defining role in CT efficiency. For an (AT)(n) bridge, the orientation of the base pairs is critical; the yield of intrastrand HT is markedly higher through (A)n compared with (T)(n) bridges, whereas HT via intrastrand pathways is more efficient than through interstrand pathways. Remarkably, for reactions through the same DNA bridge, over the same distance, and with the same driving force, HT from photoexcited Ap to G in the 5' to 3' direction is more efficient and less dependent on distance than HT from 3' to 5'. We attribute these differences in HT efficiency to variations in base-base coupling within the DNA assemblies. Thus base-base coupling is a critical parameter in DNA CT and strongly depends on subtle structural nuances of duplex DNA.
机译：大分子中电荷转移（CT）的机理模型通常关注CT能量和距离，这是控制CT速率和效率的主要参数。但是，在DNA中，DNA分子特有的功能，特别是DNA基本堆栈的结构和动力学，也对CT产生了巨大影响。在这里，我们通过检查光致淬灭的2-氨基嘌呤（Ap）作为空穴转移（HT）向鸟嘌呤（G）的结果，探讨了DNA双链体中微妙的结构变异对碱基-碱基CT的影响。光激发的Ap用作碱基堆积和CT效率变化的双重报告者。值得注意的是，DNA的独特特征，包括双螺旋的绞合和方向不对称，在CT效率中起着决定性的作用。对于（AT）（n）桥，碱基对的方向至关重要。与（T）（n）桥相比，通过（A）n产生的链内HT的产率显着更高，而通过链内途径的HT比通过链间途径的HT效率更高。值得注意的是，对于在相同距离，相同驱动力下通过相同DNA桥的反应，从光激发的Ap到5'到3'方向的HT的效率要比从3'到HT的距离更有效，并且对距离的依赖性更小5'。我们将HT效率的这些差异归因于DNA组件中碱基与碱基之间的差异。因此，碱基-碱基偶联是DNA CT中的关键参数，并且在很大程度上取决于双链DNA的细微结构差异。

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